Thin film photovoltaic (PV) modules (also referred to as “solar panels”) based on cadmium telluride (CdTe) paired with cadmium sulfide (CdS) as the photo-reactive components are gaining wide acceptance and interest in the industry. CdTe is a semiconductor material having characteristics particularly suited for conversion of solar energy to electricity. For example, CdTe has an energy bandgap of about 1.45 eV, which enables it to convert more energy from the solar spectrum as compared to lower bandgap semiconductor materials historically used in solar cell applications (e.g., about 1.1 eV for silicon). Also, CdTe converts radiation energy in lower or diffuse light conditions as compared to the lower bandgap materials and, thus, has a longer effective conversion time over the course of a day or in cloudy conditions as compared to other conventional materials.
The junction of the n-type layer and the p-type layer is generally responsible for the generation of electric potential and electric current when the CdTe PV module is exposed to light energy, such as sunlight. Specifically, the cadmium telluride (CdTe) layer and the cadmium sulfide (CdS) form a p-n heterojunction, where the CdTe layer acts as a p-type layer (i.e., a positive, electron accepting layer) and the CdS layer acts as a n-type layer (i.e., a negative, electron donating layer). Free carrier pairs are created by light energy and then separated by the p-n heterojunction to produce an electrical current.
During the production of CdTe PV modules, the surface of the cadmium telluride layer can be post-treated to wash the surface, add additional dopants to the layer, or add layers onto the cadmium telluide layer. For example, the cadmium telluride layer can be washed with a cadmium chloride solution, and then annealed to introduce chloride ions into the cadmium telluride layer. Typically, this process includes washing the cadmium telluride layer with the cadmium chloride solution at room temperature (e.g., about 20° C. to about 25° C.) then transferring the CdTe PV module to an oven for annealing.
However, the CdTe PV module is exposed to the room atmosphere after application of the cadmium chloride solution while being transported to the annealing oven. This exposure can result in the introduction of additional atmospheric materials into the solution of cadmium chloride and/or on the surface of the cadmium telluride layer. These materials can lead to the introduction of impurities in the CdTe PV module. Additionally, the room atmosphere naturally varies over time, adding a variable to a large-scale manufacturing process of the CdTe PV modules. Such impurities and additional variables can lead to inconsistent CdTe PV modules from the same manufacturing line and process.
Thus, a need exists for methods and systems for reducing the introduction of impurities and additional variables into a large-scale manufacturing process of making the CdTe PV modules.